Hydraulic structures are anything that can be used to divert, restrict, stop, or otherwise manage the natural flow of water. They can be made from materials ranging from large rock and concrete to obscure items such as wooden timbers or tree trunks.

A dam, for instance, is a type of hydraulic structure used to hold water in a reservoir as potential energy, just as a weir is a type of hydraulic structure which can be used to pool water for irrigation, establish control of the bed (grade control) or, as a new innovative technique, to divert flow away from eroding banks or into diversion channels for flood control.